Air Plan Approval; Michigan; Attainment Plan for the Detroit 2010 Sulfur Dioxide Nonattainment Area

SUPPLEMENTARY INFORMATION:

This supplementary information section is arranged as follows:

I. Why was Michigan required to submit an SO₂ plan for the Detroit area?

II. Requirements for SO₂ Nonattainment Area Plans

III. Review of Michigan's Attainment Plan

IV. Review of Other Plan Requirements

A. RACM/RACT

B. Reasonable Further Progress

C. Contingency Measures

V. What action is EPA taking?

VI. Incorporation by Reference

VII. Statutory and Executive Order Reviews

I. Why was Michigan required to submit an SO 2 plan for the Detroit area?

On June 22, 2010, EPA published a new 1-hour primary SO₂ NAAQS of 75 parts per billion (ppb), which is met at an ambient air quality monitoring site when the 3-year average of the annual 99th percentile of daily maximum 1-hour average concentrations does not exceed 75 ppb, as determined in accordance with appendix T of 40 CFR part 50. See75 FR 35520, codified at 40 CFR 50.17(a)-(b). On August 5, 2013, EPA designated 29 areas of the country as nonattainment for the 2010 SO₂ NAAQS, including the Detroit area within the State of Michigan. See78 FR 47191, codified at 40 CFR part 81, subpart C. These area designations became effective on October 4, 2013. Section 191 of the CAA directs states to submit SIPs for areas designated as nonattainment for the 1-hour primary SO₂ NAAQS to EPA within 18 months of the effective date of the designation, i.e., by no later than April 4, 2015, in this case. These SIPs were required to demonstrate that their respective areas would attain the NAAQS as expeditiously as practicable, but no later than five years from the effective date of designation, which was October 4, 2018.

For a number of nonattainment areas, including the Detroit area, EPA published an action on March 18, 2016 (effective April 18, 2016), finding that Michigan and other pertinent states had failed to submit the required SO₂ nonattainment area plans by the submittal deadline (81 FR 14736). Michigan submitted an attainment plan for the Detroit SO₂ nonattainment area on May 31, 2016, and submitted associated enforceable emission limits and control measures on June 30, 2016. These measures included Michigan Administrative Code (MAC) 336.1430 (“Rule 430”), which imposed emission limits for U.S. Steel. Subsequently, U.S. Steel challenged the legality of Rule 430 under state law in the Michigan Court of Claims, which invalidated Rule 430 on October 4, 2017. United States Steel Corp. v. Dept. of Environmental Quality, No. 16-000202-MZ, 2017 WL 5974195 (Mich. Ct. Cl. Oct. 4, 2017). Because the State's submitted attainment demonstration relied on a limitation that had become unenforceable and, therefore, could not meet the requirements of CAA sections 110 and 172, EPA could not fully approve Michigan's 2016 plan.

On March 19, 2021, EPA partially approved and partially disapproved Michigan's SO₂ plan as submitted in 2016 (86 FR 14827) (effective April 19, 2021). EPA approved the base-year emissions inventory and affirmed that the nonattainment NSR requirements for the area had previously been met on December 16, 2013 (78 FR 76064). EPA also approved the enforceable control measures for two facilities as SIP strengthening. At that time, EPA disapproved the attainment demonstration, as well as Michigan's proposed requirements for meeting reasonable further progress (RFP) toward attainment of the NAAQS, Reasonably Available Control Measures (RACM)/Reasonably Available Control Technology (RACT), and contingency measures. Additionally, EPA disapproved the plan's control measures for two facilities as not demonstrating attainment. EPA's March 19, 2021, partial disapproval started a sanctions clock under CAA section 179.

On January 28, 2022, EPA issued a finding of failure to attain (FFA) for the Detroit SO₂ nonattainment area, determining that the area failed to attain the 1-hour primary SO₂ NAAQS by the applicable attainment date of October 4, 2018, and established a requirement that Michigan submit a revised SIP by January 30, 2023, that provides for expeditious attainment of the NAAQS within the time period specified in CAA sections 179(d)(3) and 172(a)(2). 87 FR 4501, 4503, codified at 40 CFR 52.1170(e). Michigan subsequently submitted SIP revisions on December 20, 2022, February 21, 2023, December 14, 2023, and April 2, 2024. EPA is proposing here that the State's SIP submission meets the CAA requirements to provide for expeditious attainment of the NAAQS as required by EPA's January 28, 2022, FFA.

On October 12, 2022, EPA promulgated a Federal Implementation Plan (FIP) for the Detroit SO₂ nonattainment area (87 FR 61514), which satisfied EPA's duty to promulgate a FIP for the area under CAA section 110(c) that resulted from the March 18, 2016, finding of failure to submit. While EPA's FIP for the Detroit area met the requirements for SO₂ nonattainment area plans, the FIP did not relieve Michigan of the previously discussed CAA requirements to submit a plan that provides for attainment of the 1-hour primary SO₂ NAAQS for the Detroit nonattainment area. On December 20, 2022, Michigan submitted a revised attainment plan for the Detroit SO₂ nonattainment area mirroring EPA's FIP in order to remedy Michigan's 2016 plan deficiencies specified in EPA's March 19, 2021, rulemaking partially approving and partially disapproving Michigan's SIP.

Michigan's revised plan, as submitted on December 20, 2022, depended, in part, upon permits that had not yet been issued but would include limits and associated requirements for the U.S. Steel, EES Coke, and Dearborn Industrial Generation (DIG) facilities that are no less stringent than those set forth in EPA's FIP, codified at 40 CFR 52.1189. On March 23, 2023, EPA proposed to conditionally approve Michigan's plan, conditional upon the issuance of and submission for incorporation into the SIP the applicable permits for the U.S. Steel, EES Coke, and DIG facilities (88 FR 17488). Also on March 23, 2023, EPA issued an interim final determination to stay and defer sanctions in the Detroit SO₂ nonattainment area based on EPA's proposed conditional approval (88 FR 17376). However, the sanctions clock is permanently stopped only by meeting the conditions of EPA's regulations at 40 CFR 52.31(d), which EPA is proposing have been met here.

On December 14, 2023, the State submitted three applicable permits for the U.S. Steel, EES Coke, and DIG facilities. On April 2, 2024, the State submitted the final applicable permit for the DIG facility, along with a request that EPA approve its revised plan. On April 29, 2024, EPA issued a completeness letter, included in the docket for this action, determining that Michigan's submittal had satisfied the completeness criteria set forth at 40 CFR part 51, appendix V and met the requirement for a SIP submittal that provides for expeditious attainment set forth in EPA's January 28, 2022 FFA.

The remainder of this action describes the requirements that SO₂ nonattainment plans must meet in order to obtain EPA approval, provides a review of Michigan's revised plan with respect to these requirements, and describes EPA's proposed approval of the plan.

II. Requirements for SO 2 Nonattainment Area Plans

Nonattainment SIPs must meet the applicable requirements of the CAA, and specifically CAA sections 110, 172, 191 and 192. EPA's regulations governing nonattainment SIPs are set forth at 40 CFR part 51, with specific procedural requirements and control strategy requirements residing at subparts F and G, respectively. Soon after Congress enacted the 1990 Amendments to the CAA, EPA issued comprehensive guidance on SIPs, in a document entitled the “General Preamble for the Implementation of Title I of the CAA Amendments of 1990,” published at 57 FR 13498 (April 16, 1992) (General Preamble). Among other things, the General Preamble addressed SO₂ SIPs and fundamental principles for SIP control strategies. Id., at 13545-49, 13567-68. On April 23, 2014, EPA issued recommended guidance for meeting the statutory requirements in SO₂ SIPs, in a document entitled, “Guidance for 1-Hour SO₂ Nonattainment Area SIP Submissions,” available at https://www.epa.gov/sites/production/files/2016-06/documents/20140423guidance_nonattainment_sip.pdf. In this guidance EPA described the statutory requirements for a complete nonattainment area SIP, which includes: an accurate emissions inventory of current emissions for all sources of SO₂ within the nonattainment area; an attainment demonstration; demonstration of RFP; implementation of RACM (including RACT); nonattainment area NSR; enforceable emissions limitations and control measures as necessary to attain the NAAQS; and adequate contingency measures for the affected area. EPA already concluded in its March 19, 2021, rulemaking that Michigan has met the emissions inventory and nonattainment area NSR requirements.

In order for EPA to approve a SIP as meeting the requirements of CAA sections 110, 172 and 191-192 and EPA's regulations at 40 CFR part 51, the SIP for the affected area needs to demonstrate to EPA's satisfaction that each of the aforementioned requirements have been met. Under CAA sections 110(l) and 193, EPA may not approve a SIP that would interfere with or modify any applicable requirement in any area which is nonattainment for any air pollutant unless it ensures equivalent or greater emission reductions of such air pollutant. Such requirements include those concerning NAAQS attainment and RFP, or any other applicable requirement, or any requirement in effect (or required to be adopted by an order, settlement, agreement, or plan in effect before November 15, 1990).

CAA section 172(c)(1) directs states with areas designated as nonattainment to demonstrate that the submitted plan provides for attainment of the NAAQS. 40 CFR part 51, subpart G, further delineates the control strategy requirements that SIPs must meet, and EPA has long required that all SIPs and control strategies reflect four fundamental principles of quantification, enforceability, replicability, and accountability. See General Preamble at 13567-68. SO₂ attainment plans must consist of two components: (1) emission limits and other control measures that ensure implementation of permanent, enforceable and necessary emission controls, and (2) a modeling analysis which meets the requirements of 40 CFR part 51, appendix W, which demonstrates that these emission limits and control measures provide for timely attainment of the 1-hour primary SO₂ NAAQS as expeditiously as practicable, but by no later than the attainment date for the affected area. In all cases, the emission limits and control measures must be accompanied by appropriate methods and conditions to determine compliance with the respective emission limits and control measures and must be quantifiable ( i.e., a specific amount of emission reduction can be ascribed to the measures), fully enforceable (specifying clear, unambiguous and measurable requirements for which compliance can be practicably determined), replicable (the procedures for determining compliance are sufficiently specific and non-subjective so that two independent entities applying the procedures would obtain the same result), and accountable (source specific limits must be permanent and must reflect the assumptions used in the SIP demonstrations).

Preferred air quality models for use in regulatory applications are described in appendix A of EPA's Guideline on Air Quality Models (40 CFR part 51, appendix W). In 2005, EPA promulgated the AERMOD model as the Agency's preferred near-field dispersion modeling for a wide range of regulatory applications addressing stationary sources (for example in estimating SO₂ concentrations) in all types of terrain based on extensive developmental and performance evaluation. Supplemental guidance on modeling for purposes of demonstrating attainment of the SO₂ standard is provided in appendix A to the April 23, 2014, SO₂ nonattainment area SIP guidance document referenced above. Appendix A provides extensive guidance on the modeling domain, the source inputs, assorted types of meteorological data, and background concentrations. Consistency with the recommendations in this guidance is generally necessary for the attainment demonstration to offer adequately reliable assurance that the plan provides for attainment.

As stated previously, attainment demonstrations for the 2010 1-hour primary SO₂ NAAQS must demonstrate future attainment and maintenance of the NAAQS in the entire area designated as nonattainment ( i.e., not just at the violating monitor). This is demonstrated by using air quality dispersion modeling ( see appendix W to 40 CFR part 51) that shows that the mix of sources, enforceable control measures, and emission rates in an identified area will not lead to a violation of the SO₂ NAAQS. For a short-term ( i.e., 1-hour) standard, EPA believes that dispersion modeling, using allowable emissions and addressing stationary sources in the affected area (and in some cases those sources located outside the nonattainment area which may affect attainment in the area) is technically appropriate, efficient and effective in demonstrating attainment in nonattainment areas because it takes into consideration combinations of meteorological and emission source operating conditions that may contribute to peak ground-level concentrations of SO_2.

The meteorological data used in the analysis should generally be processed with the most recent version of the AERMET data preprocessor. Estimated concentrations should include ambient background concentrations, should follow the form of the standard, and should be calculated as described in section 2.6.1.2 of the August 23, 2010, clarification memo on “Applicability of Appendix W Modeling Guidance for the 1-hr SO₂ National Ambient Air Quality Standard” (U.S. EPA, 2010).

For a more in-depth discussion on the requirements of SO₂ nonattainment plans, including the use of longer-term average limits, see EPA's proposed FIP (87 FR 33095, June 1, 2022).

III. Review of Michigan's Attainment Plan

Michigan's plan for the Detroit nonattainment area mirrors EPA's final promulgated FIP for the area. Therefore, Michigan's plan relies on the modeling analysis EPA used to support its FIP, which is attached as appendix B of Michigan's December 20, 2022, submittal, to demonstrate attainment of the 2010 SO₂ NAAQS in the Detroit area. A more in-depth discussion of the modeling analysis may be found in EPA's proposed FIP (87 FR 33095) and the associated technical support document, which is included in the docket for this action as appendix B of Michigan's December 20, 2022, submittal.

An important aspect of an attainment plan is that the emission limits that provide for attainment be quantifiable, fully enforceable, replicable, and accountable. See General Preamble at 13567-68. Michigan's attainment plan includes the same limits for the U.S. Steel, EES Coke, Cleveland-Cliffs Steel Corporation, DIG, Carmeuse Lime, and DTE Trenton Channel facilities that are included in EPA's FIP, and which are all shown below in Table 1. The plan also includes the same requirement that a 170-foot stack be constructed at U.S. Steel Boilerhouse 2 by November 14, 2024, as set forth in EPA's FIP. The FIP made all of these limits and requirements that had not already been incorporated into Michigan's SIP federally enforceable via inclusion in the FIP regulatory language, codified at 40 CFR 52.1189. As Michigan's plan cannot simply rely on the limits and requirements set forth in the FIP regulatory language but must adopt them as state requirements in order for the revised SIP to be approved, the enforcement mechanisms of all the limits relied upon by Michigan's plan are described in the remainder of this section.

In preparing its 2016 plan, Michigan adopted Permit to Install 193-14A, governing the Carmeuse Lime SO₂ emissions, and Permit to Install 125-11C, governing the DTE Trenton Channel SO₂ emissions. These construction permit revisions were adopted by Michigan following established, appropriate public review procedures. The permit compliance dates were October 1, 2018, for Carmeuse Lime and January 1, 2017, for DTE Trenton Channel. Both of these permits were incorporated into Michigan's SIP as part of EPA's March 19, 2021, action partially approving and partially disapproving Michigan's SO₂ plan (86 FR 14827). The Carmeuse Lime and DTE Trenton Channel permits were incorporated into Michigan's SIP as part of EPA's March 19, 2021, action. DTE Trenton Channel has since permanently shut down as of June 19, 2022, under court order, which is included in the docket for this action. The DTE Trenton Channel permitted limit was included in the FIP analysis as a precautionary measure, so it is therefore included in Michigan's revised plan. However, any restart would require a revision to the source's Title V permit, subject to EPA review and possible objection if a permit revision would not ensure compliance with all applicable CAA requirements.

Emission limits and associated requirements for U.S. Steel, EES Coke, Cleveland-Cliffs Steel Corporation, and DIG, including the construction of a new 170-foot stack for U.S. Steel Boilerhouse 2 by November 14, 2024, are contained in permits specified in Table 1 below. These limits and associated monitoring requirements were also included in EPA's FIP, codified at 40 CFR 52.1189. The permit revisions were adopted by Michigan following established, appropriate public review procedures. EPA finds that these permit revisions provide for permanent enforceability and is proposing to incorporate these permits into Michigan's SIP in this action.